Semiconductor devices in an integrated circuit are susceptible to damages caused by electro-static discharge (ESD). ESD can be induced by the motion of static electricity generated from a non-conductive surface. For example, a human body moving on a carpet may gather thousands of volts of static electricity. Moreover, in integrated circuits testing or packaging environment, even higher static electricity may be generated. The high energy pulses of the electro-static discharge (ESD) can cause severe damage to the devices in the integrated circuits.
To prevent the damage of the integrated circuits due to the electro-static discharge, an ESD protection circuit is often included in the integrated circuit. Conventionally, in an MOS or CMOS integrated circuit, the ESD protection circuit often includes parasitic bipolar junction transistor (ex. NPN) or a silicon control rectifier (SCR) which is turned on by the high voltage pulses in an ESD event. For example, in a lateral double-diffused MOSFET (LDMOS), a conventional ESD protection structure includes a p-type contact region near a drain region of the LDMOS device. As a result, a parasitic SCR is formed by the p-type contact, the n-well, the p-substrate, the source region. Such an SCR is turned on, or triggered, to provide a current discharge path, if a high voltage at the drain contact pad is high enough to cause an avalanche breakdown at the junction between the n-well and p-substrate.
Even though conventional ESD protection structures are useful in some applications, many limitations still exist. For example, conventional ESD protection structures often have high trigger voltages. In certain applications, such high trigger voltages do not provide adequate ESD protection to the integrated circuit. These and other limitations are described throughout the present specification and more particularly below.
From the above, it is seen that an improved technique for ESD protection in semiconductor devices is desired.